Junji Furusho

New Actuators Using ER Fluid and Their Applications to Force Display Devices in Virtual Reality and Medical Treatments

We developed ER actuators with low inertia. ER actuator is a torque-controllable clutch which uses an electrorheological fluid. It is shown that this actuator has good properties for force display device, physical therapy treatment, etc. We developed new force display devices for virtual reality which use ER actuators.

Development of ER Brake and its Application to Passive Force Display

Force display systems are important in virtual reality and other applications. While conventional force displays are active systems with actuators and as such may become inherently dangerous, passive force displays are effective methods for assuring safety. In this paper, we developed a brake using electrorheological (ER) fluid, and showed a passive force display system using ER brakes with two degrees of freedom. We also discuss basic control experiments of the system.

Speed control of two-inertia system by PI/PID control

Our purpose is to develop systematic analysis and design methods for a two-inertia system. A conventional PI speed control system with a torsional load is redesigned, and the damping characteristic of the system is derived and analyzed. It is shown that the dynamic characteristic of the system strongly depends on the inertia ratio of load to motor. Three kinds of typical pole assignments with identical radius/damping coefficient/real-part are applied and compared, and the merits of each pole assignment design are concluded. Furthermore, for small inertia ratio, we show how to improve the damping by a derivative feedback of motor speed.

A 3-D rehabilitation system for upper limbs developed in a 5-year NEDO project and its clinical testing

New training methods and exercises for upper limbs rehabilitation can be developed using robotics and virtual reality technologies. The technologies can make quantitative evaluations and enhance the qualitative effect of trainings. We have developed a 3D exercise machine for upper limbs (EMUL) with special actuators using electrorheological (ER) fluid. The ER actuator is composed of an ER clutch and its driven mechanism consisting of a motor and a reduction-gear unit, and we can ensure safety of patients mechanically by using them. This paper deals with the development of EMUL. We also present the development of software for motion exercise trainings and some results of clinical evaluation.

Vibration suppression control of robot arms using a homogeneous-type electrorheological fluid

A variable viscous damper using electrorheological fluid is developed to suppress vibrations of industrial robots. An integrated system consisting of drive motor, harmonic drive, arm linkage, and electrorheological (ER) damper is experimentally measured, and it is found that the resonant/antiresonant phenomenon is effectively reduced by increasing the viscosity of the ER damper. A position control system based on the conventional semi-closed-loop control with this new type of ER damper is analyzed, and the relationship between the properties of the control system and the ER damping coefficient is discussed by means of pole-assignment technique. It is shown from analysis and experiment that the ER damper contributes both to vibration suppression and disturbance rejection.

Development of isokinetic exercise machine using ER brake

ER fluid has rheological characteristics which can be controlled by the electric field. Using particle-type ER fluid, we developed a brake device. In this study, this ER brake was used in an isokinetic exercise system for rehabilitation training under restriction of constant rotational speed of a joint during exercise. Such a passive system using a brake is basically safe for human use.

Force display system using particle-type electrorheological fluids

We developed ER actuators with low inertia. ER actuator is a torque-controllable clutch which uses an electrorheological fluid. It is shown that this actuator has good properties for force display device, physical therapy treatment, etc. Then, we developed new force display devices for virtual reality by using the developed ER actuators.

Passive force display using ER brakes and its control experiments

Force information is often required for tele-operation systems and virtual reality. Conventional force displays are active systems with actuators. This, however, is inherently active, so that it may become a danger. Consequently, passive force display is an effective method for assuring safety. The authors developed a brake using ER (electrorheological) fluid and passive force display using ER brakes. They discuss two degree of freedom passive force display and basic control experiments.

Development and experiments of actuator using MR fluid

Magnetorheological (MR) fluids are materials that respond to an applied magnetic field with a change in their rheological behavior. Though they are functionally similar to electrorheological (ER) fluids, MR fluids exhibit much higher yield strengths for applied magnetic fields than ER fluid for applied electric fields. The devices using MR fluids have an ability to provide high-torque, low-inertia, safe device and simple interface. In this study, the authors develop an actuator using MR fluid that consists of an input part, an output part and an MR-fluid clutch between them. The output part can be simply a cylinder or a disk, and thereby made extremely lightweight. In order to investigate the characteristics of the developed MR actuator, the experiments are examined.

Precise position control of robot arms using a homogeneous ER fluid

Semi-closed-loop control of a robot achieves only the control of the angular position of the motor, so it is not clear whether the end-effector is precisely positioned or not. Closed-loop control would improve positioning accuracy, but industrial robots which have elasticity in their driving systems might become unstable easily because of the noncollocated positional relationship between sensors and actuators. This study, which is aimed at realizing high-speed and high-precision closed-loop control, uses an intelligent electrorheological fluid (ER fluid). In the next section, a brief introduction is given with respect to two types of ER fluids and the development of ER dampers. Following this is a description of the experimental apparatus, which consists of an ER damper and a one-link robot arm. A discussion of its mathematical model follows. In addition, the effects of an ER damper to the resonance/antiresonance characteristics of 2-inertia systems are discussed. Next, the design of the hierarchical control system is discussed. Firstly, the design of the inner loop controller for motor velocity control is presented. As an outer loop controller, an H/sup /spl infin// controller is obtained by using a mixed sensitivity design method of robust control theory. Then it is shown that the ER damper makes the design of a high gain controller possible while maintaining robust stability. Finally, the effectiveness of the proposed control method is demonstrated by experiments.